Communication system capacity generally may be significantly improved when the transmitter has full or partial channel state information (CSI). CSI may be obtained by a transmitter via a reverse feedback channel between the transmitter and a receiver. To accommodate the limited feedback channel bandwidth, CSI normally is quantized into digital format at the receiver before being fed back to the transmitter. A codebook based algorithm generally is one of the most efficient ways to quantize the channel. A generic codebook may consist of multiple codewords. In general, the codeword is selected based on certain selection criteria and the corresponding codeword index is fed back from the receiver to the transmitter. The principles for codeword selection may be varied based on different precoding techniques.
One of the challenges of the codebook design is the balance between the feedback overhead and the quantization accuracy. Generally, the more codewords included in a codebook, the better the channel quantization accuracy. The large number of codewords, however, also means larger feedback load.
Another challenge of the codebook design is to cover a wide range of channel characteristics. For example, a correlated channel and an uncorrelated channel generally have very different properties and, therefore, come with different codebook design criteria.
Existing codebooks suffer significant challenges, however, including shortcomings in performance for both correlated and uncorrelated channels, and complexity involved in codeword searching and differential feedback. What is needed, then, is a codebook and method of using same to overcome these disadvantages in the prior art.